The invention relates to an integrated optical component, and more particularly a component having a first section comprising a wave guide perpendicular to an output facet of the component, a termination of the wave guide being coupled to this facet, and comprising a second section upstream from the first capable of being interfered with by the signal reflected by the said facet and guided by the wave guide.
The invention relates notably to laser/modulator components and advantageously applies to electro-absorption integrated optical laser/modulators and to the Mach-Zehnder laser/modulator.
An electro-absorption laser/modulator is taken subsequently for illustrating the prior art and defining the technical problem encountered as well as for defining the invention. Such components are used in applications such as long-distance optical signal transmissions.
Thus, the invention applies to any integrated optical component having a structure having the drawbacks cited above. It therefore applies in particular to laser/modulators, whatever the laser and whatever the modulator, insofar as modulation speeds ranging from 2.5 Gb/s to 10 Gb/s and more are used.
FIG. 1 depicts a diagram illustrating an integrated electro-absorption laser/modulator. This component includes a modulator section 1, preceded by a laser section 2.
The modulator section 1 is shown in detail in the sectional drawing C. There can thus be distinguished an n-doped indium phosphide InP substrate surmounted by a wave guide active layer 1 of quaternary material InGaAsP. A p-doped InP cavity 4 rests on the layer 1 and is delimited by a dielectric layer 5. Above the cavity rests a layer of a quaternary material such as InGaAsP. Above this layer is disposed an electrical contact layer 9.
The modulator section therefore comprises a wave guide 100 perpendicular to the output facet P of the component (cleaved face).
As has been said, the problem encountered with such components comes from the fact that there are reflections of part of the optical signal, on the output facet of the component, and that the reflected signal, which goes back into the guide, can interfere with the upstream sections. This is because the signal emitted by the laser and modulated by the modulator section is partly reflected by this output facet and excites the laser at its resonant frequency. The consequence is that the output signal of the component has a high level of interference and this leads to a degradation of the transmission performance.
A known solution making it possible to reduce the amount of optical power reflected consists in depositing an antireflection coating on the output facet of the component. A reflexivity of xe2x88x9230 to xe2x88x9240 dB is thus typically obtained, which is insufficient for the majority of applications. It is necessary, in particular for laser/modulators, to have xe2x88x9260 dB of reflectivity in order to avoid any excitation of the laser with this signal which is at the resonant frequency of the laser.
Another known solution illustrated by FIGS. 2A and 2B consists in adding a window 8 of indium phosphide InP at the end of the wave guide 7 buried in a substrate 3. To this end, the active cavity, i.e. the guiding layer, is interrupted before the output facet P. The light is then diffracted in this guidance interruption zone precisely as a result of the low guidance exhibited by the window thus implemented. A small amount R of signal is reflected and can return into the guide and reach the laser as can be seen in FIGS. 2A and 2B.
It should be noted on this subject that the integrated optical component fabrication methods call upon the various epitaxy techniques in order to grow layers on an InP substrate. Among these techniques can be cited the so-called MOVPE (Metal Organic Vapour Phase Epitaxy) and MBE (Molecular Beam Epitaxy) techniques.
It turns out that, whatever the epitaxy technique used, the creation of an InP window, as depicted in FIGS. 2A and 2B, at the end of the modulator wave guide, requires an additional lithography step (etching) before the final InP growth.
The implementation of an InP window at the end of the modulator wave guide therefore imposes additional steps which are an etching, and then the growth of the InP in the window.
Besides this first drawback noted with this technique, another exists as a result of the modulator/window interface. This is because this interface can create power losses or interference on the signal.
There is another solution used in a slightly different field to that of laser/modulators, which is that of semiconductor optical amplifiers. In effect, in order to avoid part of the guided and reflected signal being reintroduced into the guide in the case of semiconductor optical amplifiers, the solution consists in creating an angle between the wave guide and the output facet. Thus, the light is reflected at this angle and is consequently less guided.
However, such a solution is not sufficient for strongly guiding structures, as is the case in the integrated optical components comprising a laser/modulator, since the light remains confined in the guide despite the angle of inclination.
The object of the invention is more particularly an integrated optical component having a first section comprising a wave guide perpendicular to an output facet of the component, a termination of the wave guide being coupled to this facet, and comprising a second section upstream from the first capable of being interfered with by the signal reflected by the said facet and guided by the wave guide, principally characterised in that the said guide termination comprises an inclined guiding section and a laterally non-guiding section leading to this facet.
Thus, the wave guide is extended by an inclined guiding section followed by a laterally non-guiding section leading to the output facet of the component.
Advantageously, the inclined guiding section is of curved form.
According to another characteristic, the component has an isolation zone in order to remove the parasitic capacity effects exhibited by the laterally non-guiding section.
According to one application of the invention, the first section is a modulator section and the second section upstream of the first is a laser section, the said component having a laser/modulator function.